1. Field of the Invention
The present invention relates to a novel and advantageous process of treating heating apparatus using hot water or steam as source of heat such as water and steam baths and especially to a process of treating such apparatus serving for pasteurizing and/or sterilizing victuals or medicines which are packed and water-tightly sealed in glass, plastic, or metal containers.
2. Description of the Prior Art
It is frequently necessary to subject packed goods to a thermal treatment in a water or steam bath. Containers such as metal cans, plastic containers, preserve jars, and the like are, for instance, pasteurized and/or sterilized by heating them to a more or less increased temperature.
Such a thermal treatment in aqueous heating media can be carried out in open containers at atmospheric pressure or in enclosed systems under pressure to effect heating above the boiling point of water or in systems kept under vacuum for a gentle thermal treatment. In many cases the temperatures to which the goods in their containers are heated exceed 100.degree. C. Such a thermal treatment is required, for instance, in the production of sterilized milk and of condensed milk, of canned meat and fish, of preserves of vegetable and fruits, of dietetic food, of medicinal preparations and the like. Thereby, disagreeable side-effects such as corrosion of the containers and of those parts of the apparatus used for the thermal treatment, which are in contact with the aqueous heating medium, i.e. with steam or hot water, are encountered. Furthermore, deposits of the hardness causing salts in the water may be formed on such thermal treatment. These deposits caused by the specific composition and properties of the water used for the thermal treatment, cover the container walls as well as the packing enclosing the sterilized or pasteurized goods. In addition thereto the apparatus used for the thermal treatment are contaminated very frequently by the goods to be heat-treated either due to careless handling of the containers or to their becoming leaky or to breakage of the containers.
It is known to clean cans inserted into an autoclave, by means of a special cleaning agent as this is described, for instance, in "Der Fisch" vol. 3, page 544 (1949). It is also disclosed in German Pat. No. 617,585 to clean the empty heating apparatus by enzymatically removing milk residues. German Pat. No. 694,237 suggests to remove beer and milk scale, for instance, from pasteurizing apparatus by the addition of rather large amounts of a cleaning composition composed of tartaric acid together with smaller amounts of other salts as well as of phosphoric acid. Such scale removing compositions have an acid pH-value and thus are quite corrosive. The cleaning composition is added to remove beer, milk, and other chalk-containing scaly deposits after they have formed in the apparatus.
All these known processes, however, have the disadvantage that they do not prevent corrosion of the apparatus and the containers. Such corrosions are always encountered when using water for the thermal treatment which has a high oxygen content free carbon dioxide or, respectively, has a high content of chlorides, sulfates, and nitrates.
Heretofore, sterilizer autoclaves of different types of construction have been used for the thermal treatment of packed goods. To avoid corrosion, such sterilizer autoclaves have been equipped with anodes to be sacrificed. Another method of avoiding corrosion was the addition of sodium silicates, nitrites, chromates, sulfites, or specific types of mineral oils. However, the results achieved by the installment of such anodes or the addition of anticorrosive agents were rather unsatisfactory. Furthermore, it is evidently not appropriate to use nitrites or chromates when treating containers for victuals.
It is known from the art of water conditioning to prevent formation of calcareous fur or incrustations in aqueous systems by the addition of water soluble polyphosphates together with amino methylene phosphonates in substoichio-metric, so called "inoculating" amounts between about 0.5 mg./l. and about 25 mg./l. and as corrosion protecting agent sodium zinc polyphosphates in inoculating amounts between about 1 mg. of P.sub.2 O.sub.5 /l. and about 10 mg. of P.sub.2 O.sub.5 /l. These additives are added, however, to running water which is exposed, at the most, to a temperature up to 80.degree. C.